Anyone have thoughts on the size/capacity and duty cycle needed for a compressor that will be adequate to blow out the water lines in a 25' motorhome? I know the small one we have now won't do it. It shuts off in 2 mins or so as it has a small duty cycle.

A smaller sized compressor works fine for winterizing. Just keep the air pressure around 30PSI to avoid damaging your plumbing. I use this one from Home Despot with a pressure regulator to protect my plumbing.

I'm using my craftsman 15 gallons compressor. It has moisture collector and adjusted air pressure to 30 psi or less. It's huge, but I have long hose to reach the side of my house. Want to spend money for portable one, but it seems to work. It's also my first winterize.

I have a Dewalt, 3 gal air compressor from Lowe's that goes with us anytime we take the camper out. It's 110 V, capable to 155 lbs. I always fill it before we leave and check tires every day. Tool pressures can be turned down so I can blow out lines at around 30-35lbs without worrying about blowing apart fittings.

You only need a small tank because you pressurize the lines and only open one at a time so there is a fast squirt of air to clear it out. Open the hot water heater to drain, set the water valves for winter, drain your lines and hook up your compressor and set it for about 30#. I always used 40 with no problems but 30 is safer and works fine. Don't forget the outside shower and the toilet etc. Hang the shower hoses so they will drain and remove the heads. I broke the threads on my outside shower head because it was not removed. The other caveat is to use an oilless compressor. Not sure of the exact reasons but I would assume it has something to do with oil getting in your water lines. Be sure to pour antifreeze in your drains and gray and black tank. Turn on your water pump for about 30 seconds once early in the process and once at the end to make sure it is clear. If you are sucking antifreeze through the system a lot of this is not necessary, but I prefer not having the antifreeze in the lines, other people quite successfully use no air or use both. I go back around releasing air at least twice until there seems to be only a tiny mist at the most when you crack a valve. The whole process only takes about 15 minutes once you know the drill.

I have this small compressor that I also carry with me. It is a one gallon Campbell Hausfeld FP2028 that I bought from Ace Hardware (all stores don't carry it). It goes up to 100psi but you only need a few lbs of psi for blowing out your lines. This can be adjusted on the compressor. I have a larger Porter Cable compressor that I keep at home that can also be used.